Abstract: A counterweight mechanism for use with a weightlifting machine including first and second input cables. The mechanism includes a peanut pulley having a top wheel configured to engage the first input cable, two bottom wheels, a counterweight pulley positioned below the peanut pulley and having a counterweight pulley frame and a counterweight pulley wheel mounted therein, where the counterweight pulley wheel engages the second input cable, and a counterweight positioned below the counterweight pulley, such that the counterweight pulley is positioned between the counterweight and the peanut pulley. Two counterweight cables each have ends fixed to the counterweight pulley frame and to the counterweight, and the counterweight cables are engaged with the bottom wheels of the peanut pulley. A weight rack assembly including the counterweight mechanism may also include a removable low row assembly and/or a removable box squat assembly.